Many different signal processing systems are faced with the problem of capturing signals that emanate from different directions. Examples of such systems include Radio Frequency (RF) base stations, air traffic control systems, and satellite systems (to name a few), which either employ mechanical devices comprising an antenna that physically moves in space, or electronic devices comprising antenna elements that apply various phase shifts to incident signals, thereby effectively steering the incident signal. These electronic devices are commonly referred to as phased antenna arrays and are becoming more and more commonly used in RF sensor and communications systems because they do not involve physical motion of the antenna and are capable of moving a beam rapidly from one position to the next.
Phased arrays are conventionally implemented by applying a phase and amplitude weight to an element of an antenna array. By altering the phase slope applied across the array the pointing direction of the beam can be controlled. Alternatively a time delay is applied to an element of an antenna array; an advantage of applying time delays as opposed to a phase shift is that time is frequency independent, whereas phase is frequency dependent (for two different frequencies, the same amount of phase is equivalent to two different amounts of time and thus two different beam directions; if two signals of different frequencies are received and processed at the same time, this same amount of phase will result in the beams being steered in two different directions).
Antennas that are designed to instantaneously receive signals over a broad range of frequencies typically apply an amount of time to each element instead of an amount of phase, since this enables incident beams to be steered independently of their respective frequencies. Time delay systems essentially comprise time delay units having transmission lines of varying lengths and incoming signals are passed through various lengths in order to modify the direction of the beam. Conventional systems typically include digital devices that switch in these transmission lines, effectively adding discrete time delay “bits” to the beams. A problem with these systems is that the transmission lines occupy physical space, and, for a large array of antenna elements, many different lengths of transmission lines are required, which results in bulky and costly arrangements.